This invention relates generally to air conditioning and, in particular, to apparatus for controlling the positioning of a vent door for supplying outside air to the mixing chamber of an air conditioning unit.
Although the present invention can be used in association with a wide range of air conditioning units, it is particularly well suited for use in conjunction with a package terminal air conditioning unit (PTAC). Package terminal air conditioners are generally free standing, low profile inside units, that are positioned against an outside facing wall of a building, typically under a window or a set of windows, which serves to condition air within a defined region such as a room or an office. This type of unit, because of its ease of installation and operational flexibility, has found a wide range of applications in many types of buildings such as office buildings, apartment houses, homes, motels and hotels.
The PTAC unit conventionally contains a concealed control panel having a series of push button function switches by which an occupant can select one of a number of heating and/or cooling modes of operation. A vent door which, when opened, allows outside air to be passed into a chamber where it is mixed with conditioned air. The control and positioning of the vent door has been a problem in many of these units for various reasons.
In some PTAC units the door is positioned manually. The occupant-user, when he or she deems it necessary, will open the door to allow outside air to enter the unit regardless of the selected mode of operation. Oftentimes, the door is forgotten when the operational mode is changed and the door will remain open when outside air is no longer required. By the same token, the door may be left closed when outside air is highly desirable for efficient operation of the unit.
In other PTAC units the operation of the vent door is tied to the operational mode that is selected without regard for outside or inside conditions. For example, during extremely cold weather the door may be opened when heat is called for by the unit. Mixing of this extremely cold air outside air with the warmer indoor air forces the unit to work extremely hard in order to meet the heating demands. Under certain conditions these demands cannot be met whereupon the unit will be forced to work continually until such time as the outdoor temperatures moderate. Clearly, this procedure is wasteful in terms of energy consumption and could be avoided if further control was provided over the venting operation. The same is true on extremely hot days. Here the vent may be open when a cooling mode of operation is selected and remain open despite the load placed on the unit in cooling the added outside air.